1. Field of the Invention
This invention relates to a magneto-resistance effect device employing a mono-layer soft magnetic material and a magnetic head.
2. Description of the Related Art
Up to now, a magneto-resistance effect device employing a magnetic layer exhibiting magneto-resistance effect (MR device) is used in a magnetic sensor, a magnetic head, a rotation detection device or a position detection device, for detecting the magnetic field.
FIG. 1 shows the structure of the simplest MR device 110. This MR device 110 is comprised of a mono-layer soft magnetic material 101 of a width W and a length L with its easy axis of magnetization D.sub.e lying parallel to the width, and electrodes, not shown, are arranged on both longitudinal ends of the soft magnetic material 101. In such MR device 110, changes in resistance of the soft magnetic material 101 should be produced by an external magnetic field H.sub.ext, which should be detected as changes in voltage across the electrodes by flowing the sense current i across the electrodes.
However, measurement of magnetization on impression of the external magnetic field H.sub.ext from a direction parallel to the longitudinal direction across the MR device 110 reveals that significant hysteresis is produced, as indicated in FIG. 2. On the other hand, measurement of the electrical resistance indicates no changes in resistance with the external magnetic field Hext, as indicated in FIG. 3. This is ascribable to the fact that, since the magneto-static anisotropy of the soft magnetic material 101 in the longitudinal direction exceeds the physical magnetic anisotropy in a direction along the easy axis D.sub.e, the direction of magnetization D.sub.f of the soft magnetic material 101 cannot be oriented along the easy axis D.sub.e.
Consequently, for applying such MR device to, for example, the magnetic head, the direction of the external magnetic field H.sub.ext, which, in this case, is the signal magnetic field, is designed so as to be parallel to the easy axis D.sub.e of the soft magnetic material. In the following description, a magnetic head in which the MR device is arranged so that the direction of the easy axis D.sub.e of the soft magnetic material will be perpendicular to the direction of the external magnetic field H.sub.ext is termed the vertical type MR head, while a magnetic head in which the MR device is arranged so that the direction of the easy axis D.sub.e of the soft magnetic material will be parallel to the direction of the external magnetic field H.sub.ext is termed the horizontal type MR head. In the above-described horizontal type MR head, limitations are imposed on reducing the track width because the track width is determined by the electrode-to-electrode distance.
For constructing the vertical type MR head in which the track width is determined by the width of the soft magnetic material and in which the direction of magnetization of the soft magnetic material can be oriented in the direction of easy axis De, such an MR device has been devised in which two layers of a soft magnetic material are layered with the interposition of a non-magnetic layer. This MR device 120 is made up of a first layer of a soft magnetic material 102 and a second layer of a soft magnetic material 103, layered together with the interposition of a non-magnetic layer, not shown, with a pair of electrodes, not shown, being attached to both longitudinal ends of the soft magnetic layers 102, 103, as shown in FIG. 4.
With the MR device 120, the direction of magnetization D.sub.f of the two soft-magnetic layers 102, 103 can be oriented in the direction of the easy axis D.sub.e by exploiting the facts that the directions of magnetization D.sub.f are affected by the magnetostatic interaction between the two soft-magnetic layers 102, 103 and that a magnetic field due to the electric current Hi in a pre-set direction is generated within the two soft-magnetic layers 102, 103 by the sense current i flowing between the electrodes. With the above-described structure of the MR device 120, the external magnetic field H.sub.ext from a direction perpendicular to the easy axis D.sub.e also causes rotation of the direction of magnetization D.sub.f of the two soft-magnetic layers 102, 103, thus producing changes in resistance.
However, measurement of the magnetization on application of the external magnetic field H.sub.ext from a direction perpendicular to the direction of easy axis D.sub.e across the MR device 120 reveals that such application of the external magnetic field gives only a magnetization curve exhibiting hysteresis, as shown in FIG. 5. The electrical resistance is as shown in FIG. 6. It should be noted that the characteristics shown in FIGS. 5 and 6 are those for the width of each of the soft magnetic layers 102, 103 equal to 2.5 m, and that, if this width is reduced, both the magnetization curve and the resistance curve exhibit more acute hysteresis. For example, the resistance curve for the widths of the soft magnetic layers 102, 103 of 0.5 m exhibit significant hysteresis, as indicated in FIG. 7.
The above-described phenomenon is brought about by the difference in area between the first layer 102 and the second layer 103, as shown in FIG. 8 showing the cross-section of the MR device 120. In patterning the layered assembly made up of the first magnetic layer 102, non-magnetic layer 104 and the second soft magnetic layer 103, it is extremely difficult to etch the assembly to a vertical cross-section, such that both lateral sides of the etched layered assembly are inclined at a pre-set angle .theta. less than 90.degree..
If, in the MR device 120, there is produced a difference in width between the soft magnetic layers 102, 103, there is produced a significant difference in the magnitude of the magnetic fields produced by the magnetic poles on end faces of the soft magnetic layers 102, 103. The result is that, even in the absence of the external magnetic field H.sub.ext, the direction of magnetization D.sub.f in the soft magnetic layers 102, 103 cannot be oriented in the direction of the easy axis D.sub.e. The reason such phenomenon becomes outstanding with the decreased width of the MR device 120 is that the narrower the widths of the soft magnetic layers 102, 103 , the more difficult it becomes to override the difference in the widths of the two layers 102, 103.